add response body logging to non 2xx responses

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 5.6.1
+  - Added body and event logging in debug level for non 2xx responses [#142](https://github.com/logstash-plugins/logstash-output-http/pull/142)
+
 ## 5.6.0
   - Added standardized SSL settings and deprecates their non-standard counterparts. Deprecated settings will continue to work, and will provide pipeline maintainers with guidance toward using their standardized counterparts [#140](https://github.com/logstash-plugins/logstash-output-http/pull/140)
   - Added new `ssl_truststore_path`, `ssl_truststore_password`, and `ssl_truststore_type` settings for configuring SSL-trust using a PKCS-12 or JKS trust store, deprecating their `truststore`, `truststore_password`, and `truststore_type` counterparts.

lib/logstash/outputs/http.rb

@@ -154,12 +154,15 @@ def log_retryable_response(response)
   end
 
   def log_error_response(response, url, event)
-    log_failure(
-              "Encountered non-2xx HTTP code #{response.code}",
-              :response_code => response.code,
-              :url => url,
-              :event => event
-            )
+    log_details = {
+      :response_code => response.code,
+      :url => url,
+    }
+    if @logger.debug?
+      log_details[:event] = event.to_json
+      log_details[:response_body] = response.body
+    end
+    log_failure("Encountered non-2xx HTTP code", log_details)
   end
 
   def send_events(events)